The present invention relates to methods and systems for measuring, dispensing and spreading of powders. In particular, the invention relates to a method for measuring and dispensing a powder for use in a three dimensional printing or solid freeform fabrication system.
The construction of articles of manufacture using solid free-form fabrication (SFF) methods has been disclosed in U.S. Pat. No. 5,490,962, and in U.S. Pat. No. 5,387,380 on three-dimensional printing (3DP). These SFF and 3DP methods have the ability to construct a wide range of objects using construction materials in powdered form. A limitation in building practical devices useful for implementing SFF and 3DP methods is a powder handling system that can be used to dispense selected amounts of a variety of powders under computer or manual control, with a minimum of human intervention and with a minimum of cross-contamination between powders. The present invention is a system designed to dispense powders while satisfying these needs.
There are many arts which require the measurement of quantities of a powder and the dispensing of such powder. At times a measured powder sample is needed for blending with another powder sample. Technological arts such as pharmaceutical manufacturing, powder coating, confection manufacturing, powder metallurgy, cosmetics, spices, and flavorings are some examples of areas of technology which have a need for such powder handling methods. There is an especially important need for efficient powder dispensing and distribution in the use of SFF methods. SFF and 3DP use one or more powders dispensed from a reservoir into a container typically called a build bed to fabricate articles of manufacture. In these methods of fabrication a portion of at least one powder is transferred from the reservoir to the build bed to form a layer of powder. Various techniques are used to form a solid from a portion of the layer of powder. In the case of 3DP a binder is printed onto a layer of powder in a build bed to convert a portion of the layer from a powder into a solid. Successive portions of the same or a different powder are then dispensed and spread over an existing layer in the build bed and subjected to additional printing on selected portions of each successive layer of powder.
It has been disclosed in U.S. Pat. No. 5,204,055 that in a 3DP process a powder being applied in a layer on a build bed can be distributed from a dispensing head passing over a build bed. In U.S. Pat. No. 5,387,380 is disclosed the use of a sieve drum for dispensing powder over a build bed. Both of these disclosed systems and methods of operation suffer from problems. The thickness of a layer of powder deposited on a build bed is known in the art to be an important parameter in how well 3DP or SFF works in manufacturing an article. The thickness of a layer depends on both any method used for compacting the powder, and the amount of powder dispensed onto the build bed. The dispensing head and sieve drum disclosed in these two patents require a complicated multicomponent apparatus adapted for motion over a build bed for their operation. If only one dispensing head or sieve drum is used in a given 3DP or SFF apparatus, then the dispensing head or sieve drum used would require cleaning during a changeover to a second powder if multiple powders were used in the 3DP or SFF fabrication of an article. The complexity of the dispensing head and sieve drum and the risk of cross-contamination of powders in a multipowder 3DP or SFF fabrication method are serious disadvantages in the disclosed powder dispensing systems.
A method and an apparatus for use in 3DP were disclosed in U.S. Pat. No. 5,647,931. A method for dispensing powders, that can be used in 3DP processes, was disclosed in that patent. That method is described as having a selected powder metered from a reservoir by use of a rotating notched drum feeding device. The powder so metered is allowed to fall by gravity into a movable container. This movable container is adapted for motion above a build bed, and for distributing the powder onto the build bed. This apparatus and method both have the disadvantage of increased complexity. The apparatus disclosed uses a movable container fitted with a means for vibrating the container to distribute powder over a build bed. The movable container would need to be cleaned from time to time to ensure that powder is not retained in its interior. The movable container has a large surface area contacting the powder, and which would require cleaning. The present invention provides an apparatus and a method for measuring and distribution of powders for SFF use, that are simpler and that require less complex equipment than that disclosed in the U.S. Pat. No. 5,647,931.
A method for dispensing a powder is disclosed here which uses a rotating cylindrical dispenser to meter measured portions of a powder from a dispensing hopper. A powder dispensed from said hopper is dropped by force of gravity to a platen, said platen being movable horizontally from a first position under said hopper to a second position along a build bed container for containing powder to be consolidated into fabricated articles of manufacture. Any of the SFF methods of fabrication could be used with the invention such as but not limited to 3DP, selective laser sintering, or stereolithography. The method of the present invention discloses distribution of the powder from the platen across the build bed to distribute the powder as a layer over the upper surface of the build bed.
The rotating cylindrical dispenser may comprise a rotating cylinder having an elongate recess, and adapted for rotation from a position allowing powder flow from the hopper into the recess, to a position allowing powder flow from the recess onto the platen. This rotating cylinder is referred to as a rotating spoon. The rotating cylindrical dispenser may also comprise a rotating screw adapted to convey powder from the interior of the hopper to the exterior of the hopper, from where the powder can fall to a platen.
The system repeats the process a selected number of times necessary to deposit a selected number of layers of powder on the build bed. The number of layers is selected by the operator of the system depending on the size of the articles to be fabricated, the nature of the powder or powders used in the build bed, and the amount of detail to be incorporated into the fabricated articles.
By use of an elongate platen in the method of the present invention, multiple powders can be used in fabricating articles using SFF and 3DP. According to the teachings of the invention an elongate platen is mounted under a plurality of hoppers for containing powder. The length of the elongate platen is determined by the length of the hoppers and the distance between the hoppers, a suitable platen extending under each powder hopper being used in the method.
It is an object of the present invention to provide a method for dispensing a powder for use in SFF and especially 3DP which can be automated.
It is an object of the present invention to provide a method for dispensing multiple powders for use in SFF and especially 3DP which can be automated.
It is an object of the present invention to provide a method for dispensing multiple powders for use in SFF and especially 3DP which minimizes the number of mechanical parts necessary in an apparatus used for SFF and 3DP.
It is an object of the present invention to provide a method for dispensing multiple powders for use in SFF and especially 3DP which allows for refilling a powder dispenser while a SFF and 3DP apparatus is in operation.
It is a further object of the present invention to provide a method for dispensing multiple powders for use in SFF and especially 3DP which minimizes cross-contamination between the powders used.
A method for dispensing multiple powders is disclosed herein which can be automated and which also provides for the minimization of potential cross-contamination between the powders used. A similar method is also disclosed which can be used with only one powder. An apparatus is disclosed which enables the use of the methods disclosed. The methods and apparatus also provide for the distribution of a dispensed powder over a build bed.
The methods of the present invention consist of at least one powder dispensing hopper, a sliding platen to horizontally transport dispensed powder and a powered roller to deliver dispensed powder from the platen to a build bed.
Parts of the powder dispensing apparatus may be made of nylon polytetrafluoroethylene or other suitable materials of construction. The apparatus according to the invention is preferably made of a durable metal such as stainless steel, aluminum or an aluminum alloy. It is especially preferred that the apparatus according to the invention be made of aluminum alloy.
It has also been discovered that the invention is used to best advantage when at least one powder contacting surface of the apparatus is surface treated or is covered with a coating. Examples of coatings that are suitable for use in practicing the invention include: metal laminates consisting of metals other than nickel, an anodized finish, a hardcoat anodized finish, siloxane, baked enamel, electroplated enamel, electroless nickel, coated elastomer, laminated elastomer, dipped latex, sprayed latex, polyvinyl chloride, nylon, polytetrafluoroethylene, polyurethane, an epoxy resin, or a polyester. By latex is contemplated the use of a resin such as styrene-butadiene, polyvinyl acetate, or acrylic resins. It is preferred that a coating for use in practice of the present invention be a coating approved by the U.S. Food and Drug Administration for use in pharmaceutical manufacturing.
Advantages we have found achieved with the apparatus and method of the present invention include: providing inertness to prevent contamination of active drugs or excipients used in the SFF or 3DP processes, providing xe2x80x9cgripxe2x80x9d for the base layer in the processes, compliance with FDA regulations or USDA regulations, providing resistance to corrosion when certain active drug substances are present as a powder to extend the useful life of the machine components of the apparatus. Easier release of a finished article from a build bed after completion of a solid free-form fabrication process used to make the article, is also achieved by coating powder contacting parts of the apparatus. By the use of a properly selected coating, a less expensive metal may be used to advantage in the apparatus of the invention. For example, by using an anodized finish on an aluminum component of the apparatus, aluminum may be used for that component instead of stainless steel.
By xe2x80x9cgripxe2x80x9d here is meant the adherence of a powder layer to a surface. In using a powder process involving SFF or 3DP, a powder must be spread over a build bed. It has been found that the first few layers of the spread powder must have a certain amount of adherence to the build bed surface, usually a piston, to allow subsequent layers of powder to be readily spread over these first layers, without disturbing those first layers. A coating of a material such as a latex over the surface of the build bed or piston has now been found to provide a desirable amount of such grip.
We have now also found that combinations of coatings may be used on surfaces of the inventive apparatus to great advantage. A hardcoat anodized finish may be combined with a subsequent polytetrafluoroethylene coating to render an aluminum surface to be especially well suited for use in practicing the method of the invention. Surfaces of a powder dispensing apparatus in accord with the teachings of the present invention, that can advantageously be coated include: the hopper interior, the powder transport screw, a spreader used for conveying powder from a platen to a build bed, a rotating cylinder interior recess or rotating spoon, a piston supporting a build bed and the transport platen. The spreader is understood to be either in the form of a scraper, a doctor blade, or a roller. If a roller is used, the roller may be powered.
Combinations of different surface coatings on different powder contacting surfaces used in the same inventive apparatus are also contemplated as being encompassed by the invention. A coating according to the present invention such as a polyvinyl chloride may be desirable for use on a build bed piston to provide xe2x80x9cgripxe2x80x9d of first powder layers, and a hardcoat anodized finish further comprising polytetrafluoroethylene would be desirable on the platen or rotary powder dispenser used in the apparatus.